It was back in season 4 when John Locke gave a copy of Philip K. Dick’s VALIS
to Ben Linus but it was this week's episode, "Happily Ever After", that really showed the influence of PKD. It was Desmond-centric and cements his place as one of the best characters on the show. He is special with regards to electromagnetic radiation and is used rather sparingly. His love for Penny seems the most genuine of all the relationships and he doesn't seem to have an active daddy issue, though he does, admittedly, have a father-in-law problem. Desmond is a Lostie, but different.
In his flash sideways, all is well between him and his boss Charles Widmore. Hell, he even gets to sample the pukka scotch denied to him in "Flashes Before Your Eyes". But he is tasked with chaperoning Charley, fresh from his near overdose and a stint in a jail cell. As they're driving, the rock star grabs the car's steering wheel causing it to plunge into the ocean. Desmond escapes the sinking car and attempts to rescue Charley but the pop star merely sits there behind the glass until he puts his palm up to it. Desmond flashes back to Charley's death at the Looking Glass station and sees his hand with "Not Penny's Boat" scrawled upon it.
Eloise Hawking is Eloise Widmore in this world and Desmond and Penny do not know one another. After an MRI results in flashes back to his time with Penny, Desmond must confront Ms. Widmore about Charley's absence at a social function he was to perform at. Eloise proves to be special in her own way. While Charley and Desmond both have a gut feeling that something is amiss, Eloise seems to be above the fray and fully knowledgeable about what is going on. Desmond asks her to see a list of musicians which includes a Penny but Eloise denies him saying that it would be a violation and that he isn't ready. A violation of what?
The flash sideways world is something akin to PKD's Black Iron Prison but it's not about social or political control. I'm not sure what it's about, to be honest. Desmond has Widmore's approval while Jack seems to be living up to his father's hope that he would be a better father to his children than Christian was to Jack. For Locke, this world means coming to grips with his disability and being with Helen. On the flip side, Kate is still on the run. While unable to escape his past, Sayid still has Nadia for some consolation. Sawyer is still seeking revenge but at least he's on the straight and narrow. But Jin & Sun are obviously having problems with Mr. Paik and Keamy. There doesn't seem to be a commonality to their flash sideways plights other than not having landed on the Island.
But our Losties are beginning to see through the world of the flash sideways. As Dick would have said, they are undergoing anamnesis – they are losing their forgetfulness. For the author, it meant seeing that time had stopped in 70C.E. and a simulacrum of reality had taken its place. In LOST, we have the flash sideways with the Island underwater. If, as Jacob said, our little paradise is like a cork keeping a swell of evil and malevolence at bay, then it follows that this new "reality" is subject to those sinister forces. Could the violation Eloise mentioned be that of the universe's self-correction mechanism?
At the end of "Happily Ever After" Desmond asked Minkowski to get a hold of flight 815's manifest, the idea being that he would demonstrate to his fellow passengers that all is not what it seems and that they have a common past (present?) on the Island. I postulate that getting the rest of the Losties to understand this will be key to defeating the forces of darkness that have been loosed upon the world.